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AVR Dragon – reverse engineering

During developing you go into normal and abnormal situations. Well, during one of those abnormal ones I burned down my AVR Dragon programmer. I connected it to an equipment which had a ground potencial of around 50Vdc. So current went through the ISP/USB.

The consecuence was a burned USB controller, a smoked ISP cable and a seemingly burned programmer.

The AVR Dragon is supported by two CPUs, one ATMega128 and one ATMega2560. The Megal128 is the primary MCU and the Mega2560 is the secondary. During the flashing of a new FirmWare, the primary is programmed first and then the secondary.

Searching in the Internet I found two sources from which it was possible to get something…

http://www.aplomb.nl/TechStuff/Dragon/Dragon.html
A common failure is when the converter TPS61020DRCRG4 goes off. To fix this it is enough just to jump it (in case that we are not using high voltage programming HVPP) and this is very well explained in the russian instructions.

In my case the failure was more complicated. The primary processor was OK. With the second was possible to communicate (it was possible to burn the FW) but not through the ISP 🙁

The only components inserted between the CPU and the programming peripherial are resistors and a couple of transistors BC857 and all of them were OK. So just remains the port on the secondary CPU (2560). This can be changed of course, but we can not keep the original bootstrap 🙁

By chance Franta OK2JNJ had also a “dead” AVR Dragon in his drawer. This one had the secondary 2560 in good shape, so it was just enough to change it. Because of the fact that the tracks on the PCB are under 8mil (0.2mm) wide, the repairing is very hard. After the change of the 2560 the Dragon came back to life 🙂

A lot of the success is due to Franta OK2JNJ because, without his “casualty”, the repair could not be done.

Due the fact that I could not find in the Internet information about this
Dragon, I used a wrong one to get access to the interconnect between the
MCUs and the rest. What I did was to remove all the components and
remove the protecion cover (mask). With the board “clear” I was able
to find out the problem.

Attached are the pictures and I hope this will hep someone with a similar
problem.

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